A toroidal vortex is a donut of rotating fluid. The most common example is a smoke ring. It is basically a self-sustaining natural phenomenon. FIG. 1 shows toroidal vortex 700 at an angle, sliced in two to illustrate airflow 701. In a section of the vortex, a particular air motion section is shown by stream tube 702, in which the air constantly circles around. Here stream tube 702 is shown with mean radius 703 and mean speed 704. The circular motion is maintained by a pressure differential across stream tube 702 (i.e., the pressure is higher on the outside than the inside). This pressure differential, Δp, by momentum theory, is given by the equation Δp=ρV2/R where ρ is air density, R is mean radius 703, and V is mean speed 704. Thus, the pressure continually decreases from the outside of toroidal vortex 700 to the center of the circular cross-section, and then increases again towards the center of toroidal vortex 700. The example shows air moving downwards on the outside of toroid 700, but the airflow direction can be reversed. In this case, the pressure profile remains the same. The downward outside motion is chosen because it is the preferred direction for use in the nozzles disclosed herein.
FIG. 2 graphically represents a typical pressure profile across a toroidal vortex. Shown is the pressure on axis 801 as a function of distance in x-direction 802. Line 803 indicates atmospheric pressure, which remains constant along x-direction 802.
The toroidal vortex nozzles disclosed herein were developed from the technology embodied in toroidal vortex attractors previously described in Applicants' application entitled “Toroidal and Compound Vortex Attractor,” which is incorporated herein by reference. FIG. 3 shows a toroidal vortex attractor 900 that has motor 901 driving a centrifugal pump located Within outer housing 902. The centrifugal pump comprises blades 903 and backplate 904. This pumps air around inner shroud 905 such that the airflow forms a toroidal vortex circulating around inner shroud 905. Flow straightening vanes 906 are inserted downstream from the centrifugal pump between inner shroud 905 and outer housing 902 in order to remove the tangential component of the airflow. Thus, air travels around inner shroud 905 radially with respect to the centrifugal pump.
Air pressure within outer housing 902 is below ambient pressure. The pressure difference between ambient air and air within outer housing 902 is maintained by the curved airflow around the lower, outer edge of inner shroud 905. Here, the downward flow between inner shroud 905 and outer housing 902 is guided into a horizontal flow between inner shroud and attracted surface 907. This pressure difference is given by ρv2/r where v is the speed of air 908 circulating around inner shroud 905, r is radius of curvature 909 of the airflow, and ρ is the air density. The maximum air pressure differential, which depends upon the centrifugal pump blade tip speed V at point 910 and tip radius 911 R, is given by the equation ρV2/R.
Toroidal vortex attractor 900 can be thought of as a vacuum cleaner without a dust collection system. Dust particles are picked up from attracted surface 907 by the high speed, low pressure airflow. Because no dust collection system is provided, the dust particles circulate within toroidal vortex attractor 900.
Likewise, the toroidal vortex vacuum cleaner is a bagless design in which airflow is contained. Air continually circulates from the area being cleaned, through the dust collector, and back to the area being cleaned. Specifically, the contained airflow circulates from a vacuum cleaner nozzle, to a centrifugal separator, and back to the nozzle. A centrifugal dust separator may be used such as the one disclosed in Applicants' application Ser. No. 10/025,376, entitled “Toroidal Vortex Vacuum Cleaner Centrifugal Dust Separator,” filed Dec. 19, 2001, now U.S. Pat. No. 6,719,830, which is herein incorporated by reference. Since dust is not always fully separated, some dust will remain in the airstream heading back toward the nozzle. The air already within the system, however, does not leave the system, thereby preventing dust from escaping into the atmosphere. In addition to ensuring an essentially sealed operation while the nozzle contacts a surface, the toroidal vortex vacuum cleaner's operation also remains sealed when away from a surface. Sealed operation away from a surface is important because it prevents the vacuum cleaner nozzle from blowing surface dust around and from ejecting unseparated dust into the atmosphere.
Applicants' toroidal vortex attractor is coaxial and operates such that air is blown out of an annular duct and returned into a central duct. This direction of airflow is necessary for correct operation of the toroidal vortex attractor. To demonstrate the effects of the reverse airflow, FIG. 4 is provided. System 1000 comprises outer tube 1001 and inner tube 1002 in which air passes down central delivery 1004 and returns up air return duct 1005. While it would be desirable for the outgoing air from central delivery duct 1004 to return into air return duct 1005, a simple experiment shows that this does not happen. Air from central delivery duct 1004 forms plume 1007 that continues on for a considerable distance past the opening of delivery duct 1004 before dispersing. Thus, air 1006 is sucked into the air return duct from the atmosphere. This flow design is clearly unsuited for a sealed vacuum cleaner design.
FIG. 5 shows system 1100 having the reverse airflow of FIG. 4. Again, system 1100 comprises outer tube 1101 and inner tube 1102 (which form central return duct 1105). Air is blown down outer delivery duct 1104 and returned up central return duct 1105. Air 1107 blown from outer delivery duct 1104 must be replaced by sucking air into central return duct 1105. This leads to a low-pressure zone at A. The low-pressure zone at A causes air from outer air delivery duct 1104 to bend inward. Thus, the air (whose flow is exemplified by arrows 1107) is forced to turn around on itself and enter central return duct 1105. Such action is not perfect, and some air 1108 escapes at the sides of outer delivery-duct 1104, and is replaced by the air 1106 being drawn into central return duct 1105.
FIG. 6 shows air returning from outer delivery duct 1104 into central return duct 1105 with radius of curvature 1203 (“R”) and airspeed V at location 1204. With airspeed V at location 1204, the pressure difference between the ambient outer air and the inside the system is ρV2/R, where ρ is the air density. The airflow at the bottom of the concentric tubes is in fact half of a toroidal vortex with the other half at the top of the inner tube 1102 within outer tube 1101. The system of FIGS. 5 and 6 is thus a vortex system with a lower than atmospheric pressure in the central return duct, and a higher than atmospheric pressure in the outer delivery duct. There is minimal mixing of internal and atmospheric air.
The simple concentric nozzle system shown in FIGS. 5 and 6 can be optimized into effective toroidal vortex vacuum cleaner nozzle 1300 depicted in FIG. 7. Inner tube 1301 is thickened and rounded off at the bottom (inner fairing 1306) to provide smooth airflow from air delivery duct 1302 to air return duct 1303. Outer tube 1304 extends below inner tube 1301 and curves inward such that air from delivery duct 1302 is redirected toward the center of toroidal vortex vacuum cleaner nozzle 1300. This minimizes the amount of air escaping from the main flow. The nozzle has flow straightening vanes 1305 to prevent the downward airflow in air delivery duct 1302 from corkscrewing. Corkscrewing may cause air to be ejected from the bottom of the outer tube 1304 due to inertia. When compared to other approaches, the vortex vacuum cleaner nozzle 1300 has less leakage and a much wider opening for the high speed air flow to pick up dust.
The vortex nozzle in its basic form is circular in cross-section, but it may take on other shapes. FIG. 8 shows rectangular nozzle 1400 terminating with inner fairings 1401 that are attached to outer tube 1402. Air is delivered via delivery duct 1403 and returns via return duct 1404. Flow straightening vanes are omitted for clarity, but are, of course, essential. Alternatively, the flat ends of rectangular nozzle 1400 may be curved such that the nozzle has a more oval-shaped cross-section.
FIG. 9 depicts the combination of a vortex nozzle and a centrifugal dirt separator, thereby yielding complete toroidal vortex vacuum cleaner 1500. Again, air ducts are created by concentrically placing inner tube 1507 within outer tube 1508. Airflow through outer air delivery duct 1502, inner air return duct 1503, and toroidal vortex nozzle 1506 (comprising flow straightening vanes 1504 and inner fairing 1505) occurs as described previously in FIGS. 6, 7, and 8. Centrifugal air pump (as in the toroidal vortex attractor of FIG. 3), comprising motor 1509, backplate 1510, and blades 1511, circulates air through the system. Air leaving blades 1511 spins rapidly such that dust and dirt are thrown out to the cylindrical sidewall of outer casing 1512. Air moves downward and inward along the bottom of dirt box 1501 such that dirt is precipitated. The air then flows upwards over dirt barrier 1513 and subsequently down the outer air delivery duct 1502. At this point, the air is clean except for fine particulates not deposited in dirt box 1501. These particulates circulate through the system repeatedly until they are captured in dirt box 1501. After use, the dirt that has been collected in dirt box 1501 can be emptied via dirt removal door 1514.
Toroidal vortex vacuum cleaner 1500 may utilize circular nozzle 1506, but the system works equally well with rectangular nozzle 1400 of FIG. 8. Various nozzle shapes can be designed and will operate satisfactorily provided that the basic cross-section of FIG. 7 is used.
Airflow across toroidal vortex nozzle 1506 from outside the system will become entrained with the internal airflow due to air friction effects to form a “plume” of air that is deleterious to the vacuum nozzle action. The effect is illustrated in FIG. 10. This shows a vortex nozzle comprising outer tube 1602 and inner donut 1601. Air flows downward between inner donut 1601 and outer tube 1602. The airflow follows the form of inner donut 1601 and turns upward through the center of inner donut 1601. Air flowing across the bottom of inner donut 1601 contacts air outside the nozzle across the opening of outer tube 1602. Friction effects between this outer air and the air moving inside the nozzle across the opening in 1602 causes outer air (shown by air streams 1603) to be drawn across the nozzle opening to the center. When air streams 1603 meet at point A, they form a high pressure stagnant point A, and air is forced to turn downward to form air plume 1604. It should be noted that air plume 1604 is formed from air outside the nozzle and there is no mixing of outside and internal air. This has been verified by computational fluid dynamics.
Plume formation is not affected by internal pressures within the nozzle. Generally speaking, the pressure in the center of the tube formed by inner donut 1601 is below atmospheric pressure whereas the pressure in the air flowing down between outer tube 1602 and inner donut 1601 is above atmospheric pressure. This air follows the curve at the bottom of inner donut 1601 regardless of internal pressures providing that the amount of air flowing up within inner donut 1601 is exactly the same as that flowing down between inner donut 1601 and outer tube 1602. Air plume 1604 is undesirable because although it contains only the concentration of dust present in the local environment, it will blow away dust underneath the nozzle.
Thus, there is a clear need for a simple vortex vacuum cleaner nozzle that addresses the problem of plume formation.